1. Technical Field
This invention relates to dispensing pumps and, more particularly, to locking and unlocking improvements with respect to those pumps in which the plungers are locked down in fully depressed positions for shipment and shelf storage purposes.
2. Background Art
Lock down dispensing pumps are not new per se. See for example prior U.S. Pat. No. 4,369,899 owned by the assignee of the present invention.
While such locking arrangements, in which a radial lug or ear on the plunger is trapped beneath an overhanging ledge of the pump collar, have proven quite effective, there is nothing in that construction to inhibit or restrict unlocking of the plunger except for the frictional drag which is inherently created between the lug and the overhanging ledge of the collar.
Furthermore, in the event the pump uses a return spring for the plunger, there is nothing in such arrangements to prevent rather instantaneous extension of the plunger once the locking lug has been released from beneath the ledge, and such instantaneous extension has an adverse effect upon the ability of the pump to become fully primed in preparation for a subsequent depression stroke by the user. It has been found in this respect that a relatively slow, controlled extension of the pump from its locked down position is considerably more conducive to drawing a full charge of liquid into the pump chamber in a priming action than is true when the plunger is suddenly extended such as by the force of a relatively strong return spring within the body of the pump.